We propose to complete the construction and validation of the anatomical robotic finger within the R21 funding structure as a way to continue this research using the R01 funding structure to investigate the human hand neural strategies and to help design FES and prosthetic hand controllers. We will focus on completing and validating the robotic index finger. The specific aims of this proposal are to: 1) Incorporate the robotic skin that will be used as the feedback device during object exploration for the index finger. This will complete the mechanical construction of the robotic finger. 2) Identify the system component (the relationship between external force perturbation and joint displacement before cortical feedback) for both the anatomical robotic index finger and the human index finger. We will compare these components and iterate on the robot's mechanical design. 3) Identify the active system component (the relationship between muscle tension (motor current) and joint displacement) for the robotic index finger given no external perturbation. Using this active system identification database, we will determine combinations of muscle tensions that would achieve a specified movement trajectory. Furthermore, we will select several cost functions that could be used to achieve good engineering solutions to control this robotic finger. When we accomplish the above, we will have the first mechanical model of the index finger that can be controlled using "engineering" solutions. Once this system is constructed, we will be able to compare between the biological and the engineering solutions used to achieve the same finger movement. This comparison will allow us to infer the muscle synergy and optimization criteria used in the nervous system. In addition, we will be positioned to investigate the neural control of the movement with the robotic index finger during object manipulation with cutaneous feedback. For example, we will be able to investigate the neural control strategies used when pushing objects of different weights and sizes from one place to another. We will also explore how we take advantage of the finger's passive mechanisms to manipulate objects. Finally, we will be able to expand our system to include the thumb to analyze pinching, other fingers to study the relationship between different finger interactions during manipulation, and the palm to understand the role of the palm during manipulation. We believe that this hand will not only be a tool to investigate the neural control of movement, but it will also be used as a foundation to construct a future prosthetic device that will seamlessly communicate with the nervous system.